<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Page Title</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>

</head>

<body>


    <div id="box">

        <select v-model="select">
          <option disabled value="">请选择</option>
          <option>A</option>
          <option>B</option>
          <option>C</option>
       </select>
        <span>Selected: {{ select }}</span>

        <hr>

        <select v-model="selected" multiple style="width: 50px;">
            <option>A</option>
            <option>B</option>
            <option>C</option>
          </select>
        <br>
        <span>Selected: {{ selected }}</span>

    </div>

</body>
<script>
    var vm = new Vue({
        el: '#box',
        data: {
            selected: '',
            select: ''
        }
    })
</script>

</html>